Development of a PhD scientist starts with a post-doctoral position or in an industrial/acadenia environment with strong scientific knowledge where people are willing to share information.

That's true.

More knowledge of subject with good understanding and excellent ability to express and explain, makes one expert.

Competent researchers only should be permitted to be PhD supervisor to make sure good quality is produced for future.

Often PhD students go through a lot of unwanted struggle, which can be avoided and the time to complete the thesis can be reduced. This will make researcher more confident and motivated to undertake future research.

Eventually, a better expertise will be developed.